A tire changing machine is known to comprise a base, typically having the shape of a parallelepiped, and having a horizontal platform mounted thereupon, which is adapted to be rotatably actuated and to receive the wheels of a vehicle lying thereupon, and locked by appropriate lock devices, in a typically horizontal position, for tire mounting and demounting. Conventional pedals are placed on a front side of the base, for controlling the functions of the tire changing machine, and a tool-holding column rises from an opposite rear side of the base and has a hinge connection at its top, for a proximal column-facing end of a horizontal operating arm which pivots in cantilevered fashion in a rotation plane parallel to the platform. The operating arm in turn supports, at its opposite distal end, an additional connection in the form of a vertical sleeve, in which a rod having a polygonal section is slidably and non-rotatably coupled, which rod has a connection at the base-facing bottom end, for interchangeably attaching a set of work tools, to be used for mounting and demounting tires to and from respective rims of vehicle wheels. As mentioned above, the operating arm can pivot in cantilevered fashion and may be rotatably actuated either by a manual action of the tire repairer or by means of a fluid-dynamic actuator, which is placed between the arm and the top of the tool-holding column and is actuated by the special pedal control operated by the tire repairer: the operating arm is actually displaceable between a work position in which it is rotated toward the platform and a rest position in which it is laterally moved away from the platform, typically toward the right side of the front work position of the tire repairer with respect to the base. During the process of demounting or mounting the tire from or to its rim, the operating arm is pivoted into the work position relative to the tool-holding column through an angle whose amplitude is determined by the diameter of the rim and the corresponding tire, for accurate vertical alignment of the rod and especially the work tool supported thereby at the bottom end, typically a debeader, on the selected point of contact with the tire bead, which is typically sealingly placed against the edge of the rim, for removing it from the latter, without touching it to avoid damages. Therefore, the orientation of the operating arm is a critical step of the tire demounting or mounting process and requires accuracy and precision on the part of the tire repairer. These orientation and displacement steps shall be further repeated for each wheel that has to undergo tire demounting or mounting, and each time alignment must be repeated by the tire repairer with the utmost precision.
This prior art suffers from certain drawbacks.
A first drawback is that accurate orientation of the operating arm into the work position is typically a question of skill of the tire repairer, and since this operation is typically repeated many times in a work-day, tire repairers, in spite of their familiarity with it, tend to perform it in routine fashion and as quick as possible, thereby neglecting accuracy in orienting the operating arm. For this reason, during debeading, any accidental contact between the edges and the work tools held by the operating arm, due to inaccurate orientation of the operating arm, will cause damages to the edges of the rims.
A second drawback is that proper orientation of the operating arm must be repeated, even considering the difference in wheel diameters, and this step requires each time a considerably long operating time, which will be multiplied by all the wheels to be treated by tire repairers in a work-day, and becomes a remarkably long time, during which no demounting or mounting can be performed, leading to a reduction of the overall number of demounting and mounting operations, and hence of the earnings resulting therefrom.
A third drawback is that, even when tire repairers mount and demount tires to and from a set of wheels having the same diameter, e.g. the wheels of a single vehicle, they shall repeat the step of orienting the operating arm into the work and displaced positions for each of them, which leads to the above mentioned drawbacks.
A fourth drawback is that, during debeading and mounting, the tire repairer is required to hold the wheel and manipulate and position it as needed and, at the same time, to control the functions of the tire changing machine with the feet to operate the pedals located on the front side of the base. It shall be noted in this respect that the tire repairer is typically obliged to work in a lateral position relative to the expected front work position, due to the presence of the operating arm projecting out of the right side of the tire changing machine. This will affect convenient operation of pedals located on the front side of the base, and the tire repairer is thus required to assume unnatural and forced positions to perform all the actions required for tire demounting and mounting.
A fifth drawback is that certain tires have very rigid beads and debeading becomes difficult and laborious for tire repairers, who will have to manually bend the beads to introduce the lever that is usually employed to lift a portion thereof between the latter and the rim edges for the debeading tool supplied with the tire changing machine to be later introduced into that portion.